I first performed bimanual phacoemulsification approximately 25 years ago using the Girard system. Shortly thereafter, my colleagues and I modified the Mackool-Heslin Ocusystem (Surgical Design Corporation, New York, NY) in order to separate the ultrasonic tip from the infusion source. The concept was to perform the procedure through a smaller incision, but the problem was that there was no desirable reason to perform surgery this way. The current incision size required for phacoemulsification with a combined infusion/ultrasonic tip is approximately 2.7 mm. Today's IOLs can be readily inserted through such incisions, and measurements performed by myself and other surgeons consistently indicate a post-IOL insertion incision diameter of 2.8 to 2.9 mm. Most surgeons use a sideport incision, the size of which is not clinically significant (mine measures 0.7 mm externally and 0.35 mm internally).
Weighing the Advantages
Commonly, there is approximately 0.5 D of flattening of the meridian in which the surgeon makes the phaco/IOL incision. This effect is more often beneficial than detrimental—nearly always so if the surgeon makes the incision in the steep axis. These small incisions create no significant incidence of postoperative leakage or failure, and unless significant patient advantages result from reducing the incision further, there is no reason to advocate smaller incisions. The oft-quoted “waiting for the injectable IOL” statement remains pie-in-the-sky, and is simply not on ophthalmology's radar screen. Even if an injectable IOL were available, it could only be used in an eye that had a relatively small capsulorhexis. The bimanual technique, as currently performed, would require two openings in the capsule (one for infusion and one for the ultrasonic needle) for the simple reason that the capsular sac must be kept inflated during cataract removal. Would it be better to have two small incisions in the capsular sac than one slightly larger incision through which infusion was delivered during the procedure? The answer to that is obviously not known, and would probably depend upon the injectable IOL material.
With regard to increased access to nuclear material, bimanual phacoemulsification falls short here as well. In the rare instance that a problem such as zonular dialysis requires that the phaco incision be moved to a different location, this change can be accomplished with standard phacoemulsification equipment. Otherwise, phacoemulsification tips (which seal the phaco incision, prevent incisional leakage, reduce flow through the eye, and prevent the migration of nuclear particles to the region of the phaco incision), offer significant advantages over the bimanual technique. This is due to the fact that significant incisional leakage is virtually mandatory with the bimanual technique, thereby increasing the likelihood of nuclear particles flowing to one or both of the incisions required. The surgeon who feels that he has the ability to exchange the location of the infusion and ultrasonic tip locations in order to approach these nuclear particles may be correct. Unfortunately, however, he has created the problem that requires the instruments to be exchanged.
Disadvantages Worth ConsideringThere are significant disadvantages to the bimanual phaco technique. In no particular order, they are:
1. The procedure is slower. This is not universally true for all surgeons, however. Those who already use relatively low flow and vacuum levels (this is mandatory with the bimanual technique) will not notice any significant slowing of their already relatively lengthy procedure. Those surgeons, who are mainly very experienced and efficient and use flow and vacuum levels that are toward the high end of the spectrum, will become somnolent during bimanual phacoemulsification. I typically use an aspiration flow rate of 60 cc/min and vacuum levels of 600 mm Hg or greater with the Advantec Legacy unit (Alcon Laboratories, Fort Worth, TX) and the Kelman/Mackool Flare Tip. It would be extremely difficult to perform bimanual phacoemulsification using parameters that were half as great as these. Because flow and vacuum levels must be kept relatively low, followability of nuclear particles to the tip is not as great, high vacuum cannot be used to aspirate them and assist in the removal process, and greater amounts of ultrasonic energy must therefore be used. For example, I routinely utilize only aspiration (no ultrasound) to remove grade 1 to 2 nuclear cataracts with the Advantec Legacy, and this is not possible with bimanual phacoemulsification.
2. The concept that somehow a separate infusion source will drive nuclear particles to the phaco tip is untrue in my experience. In fact, the opposite is commonly the case, as the infusion cannula can frequently deliver fluid that is perpendicular to the axis of the ultrasonic tip. Guess what this does to nuclear particles that might otherwise be attracted to the tip? In contrast, the two infusion ports that are used to deliver fluid from the malleable infusion sleeve around an ultrasonic tip are ideally located for the task of promoting particle attraction to the phaco tip. In a well-designed ultrasonic tip, the infusion sleeve should taper down tightly upon the ultrasonic needle so that infusion fluid does not flow directly against particles that would be on their way to the ultrasonic needle. This has been achieved with all reasonable infusion sleeve designs. The two infusion ports therefore direct fluid toward the recesses of the chamber and create a vortex in which fluid returns to the ultrasonic tip and assists in attracting nuclear particles.
3. The flow and vacuum parameters must be greatly reduced with the bimanual technique due to the limited infusion flow/capacity of the second instrument. The reader may wish to perform the following experiment, which will prove the validity of the above statement. Attach a 20-gauge disposable needle to the infusion line of a phacoemulsification system. With the infusion bottle height at any predetermined level, measure infusion flow (if the distance between the drip chamber and the tip of the needle is 17 inches, a 20-gauge needle will deliver approximately
15 cc/min. Using a 19-gauge needle will increase this flow to approximately 30 cc/min). Now repeat the procedure using the phacoemulsification instrument that you currently employ. You will now understand why bimanual phaco must be performed using such low parameters (those of you using the larger 1.1-mm flare tip will understand why you can use flow and vacuum levels that are much greater than any other instrument available).
Summing It Up
Of course, there is a learning curve associated with bimanual phacoemulsification, and also special equipment for the surgeon to purchase. The bottom line is that if there were truly advantages to this technique, we would all flock to it. Here is my prediction—bimanual phacoemulsification dies a quiet death now, just as it did 27 years ago.
